Solo or single-cam compound bows are well known in the art. A plurality of these have been previously disclosed, some of which are described in U.S. Pat. Nos. 5,505,185 and 5,368,006, both of which are incorporated by reference as if fully set forth herein. Dual-cam compound bows are also well known in the art, some of which are described in U.S. Pat. Nos. 4,739,744 and 5,040,520, both of which are incorporated by reference as if fully set forth herein, and in which are described in detail the mechanics of a compound bow including non-circular dual cam members which impart dynamic forces on the bow limbs.
Whether single-cam or dual-cam, the purposes and advantages of compound bows are well known to those skilled in the art and need not be repeated herein. Compound bows typically are comprised of: a handle from which resilient bow limbs extend oppositely; pulley means comprising cams, levers, and/or pulleys and typically being disposed at the tips of the limbs of the bow; and one or more cables coupled to the bow limbs and/or pulley means to give assorted mechanical advantages.
When a bow is drawn potential energy is stored in the bow limbs which are deflected substantially equally when the bow string (or draw cable) is drawn. Stored potential energy may be calculated from the draw force as a function of draw distance. Potential energy is converted to kinetic energy when the archer releases the drawn bow with the arrow placed on the draw cable, thereby allowing the bow limbs to return to their resting position and propelling the arrow. Kinetic energy may be calculated from the speed and mass of the arrow, which may in turn allow the efficiency (i.e., the fraction of potential energy converted to kinetic energy) of the bow to be calculated. It is well accepted in the industry and within the sport that efficiency is critical to bow performance: the more efficient a bow the faster the bow will propel an arrow of given weight for a given draw length and given peak draw force. Previous compound bows, single- or dual-cam, have AMO standard efficiencies of approximately 70-81% (see Table 2 on page 80 of "Bowhunting World, August, 1995, which is incorporated by reference as though fully set forth herein; see Table 2 on page 68 of "Bowhunting World" December, 1996, which is incorporated by reference as if fully set forth herein; see FIG. 3 on page 62 of "Bowhunting World" April, 1997, which is incorporated by reference as if fully set forth herein; and see Table 2, Bowhunting Buyers Guide, 1997, which is incorporated by reference as if fully set forth herein). A number of bow characteristics impact the efficiency of a bow, but many of these are well known in the art and therefore need not be repeated herein. The power cam in a single-cam compound bow (or the power cams in a dual-cam compound bow) plays a critical role in bow performance and efficiency. The power cam substantially determines the rate of and total amount of deflection of the bow limbs. There is clearly an industry need and demand for more efficient bows and specifically power cam designs which render more efficient compound bow performance. The preferred embodiment of the present invention has an AMO standard 30" draw efficiency of at least 82% and has achieved an efficiency of 94%.
Previous pulley assemblies, on either single-cam or dual-cam compound bows, typically include a base cam and a power cam module mounted to the base cam, which is rotatably mounted on the bow limb tip. Different power cam modules may be used for different draw lengths and different peak draw force. Specifically, the pulley assembly typically comprises a base cam with either one or two grooves in the perimeter portion of the base cam and one or more posts, typically on the power cam side of the base cam. As is well known in the art the posts secure the ends of the bow cable sections. A power cam module is typically mounted to the power cam side of the base cam.
Previous compound bows, single- or dual-cam, with an AMO standard 30" draw have pulley assemblies which rotate between approximately 235 and 275 degrees. The preferred embodiment of the present invention includes a power cam and base cam design which with an AMO standard 30" draw results in cam rotation of no more than approximately 210 degrees, resulting in quicker (arrow speed) and more efficient (potential energy vs. kinetic energy) bow performance. This arises from the oblong shape of the power cam disclosed herein, which is novel and unobvious for a power cam for a compound bow.